Manufacture of aldehydes by the pyrolysis of acetals



MANUFACTUREQF BY THE PYRoLYsIs. or AcEr Hugh J. Hagemeyer, Jr., andMilton A. Perry, Kingsport; Tenn., assignors to: Eastman Kodak Company,Rochester, N. Y., a corporation of'New Jersey No Drawing, ApplicationMay 6,.1953, Serial No. 353,425

14: Claims. or 260601) The present invention relates. to, thepreparation of aldehydes. More particularly, the. invention is.concerned with the catalytic pyrolysis of acetals to produce:v aidhydes.

It has been low temperatures, e. g. from 40 C. 11910300. 0., thecatalytic pyrolysis of acetals leads to, the; formation. of alcohols andunsaturated others. In one, specific,- embodiment of. this, method,precious metal catalysts, e. g.- silver, gold and platinum. metals, areemployed; to. in: crease the. yield of ethe It is also known that.pyrolysis of a'cetals at higher temperatures results. in; the.tonnation. of products. of. decomposition. of: the. intermediate etherand alcohol. For instance, it is. known that. over certain catalysts.the. pyrolysis. under certain. experimental the production. ofhydrocarbons, water, hydrogen, carbon monoxide and. methane- We have nowfoundthat with, suitable contact Inaterials heated to temperatureswithin. a, relatively high range acetals. may be. converted directly toaldehydes if passed. in. the vapor phase over. he contact ma erial for aperiod of relatively sh rt duration.

known for some. time that at relatively Our discovery, besides providinga: new proeess for the preparation of aldehydes, serves to formaldehydes of longer carbon chains than, those employed. in; preparationof the acetal starting material. The. new, me hod Qf aldehyde synthesisvadvantageously avoids celftaindefiects in the prior methods ofsynthesis. parison to the aldol process, the prises an improvement inthat no required. The invention,

n tant. method. com hydr gena n s ep: s as a further i1lustrati0n,,malres possible the synthesis of Propionalfclehyd'e from, the start. ingmaterials me hanol, and. acetal ehyde. by means at the intermediateformation of dimethyl aoetal followed by the, pyrolysis thereof productsof propibnaldehyd'e.

Accordingly. t. s a p mary o je t of. theprese t in: vention to providea new method, for the Synthesis of aldehydes. A further object is. to,provide for the, syn. thesis. of aldehydes of longer :chain, length thanthe starte p r ic larly adv n g ous cont ct: ma: terials and methods ofusing; them; to. produce aldehydes by the pyrolysis of acetals. Otherobjects; will be obvious from a consideration of the accompamn'ngspecification and claims;

The objects: are accomplished by the invention whi'eh contemplates amethod comprising the steps of (A)- passing the vapor of an, aeetalofthe formula able contact material having a temperature withinthe rangeof 375 -600 C, and QB): recovering by distillation For. instan e, in.QQIIL heml ehyoe was; 21 with an.

H 2,759,979 Ce Patented Aug. 21, 1956 2 from a product mixture thus:formed an aldehyde having the formula- R'GHzCHRGHO wherein R. and- Rare. as designated above.

The direct pyrolysis of acetals to aldehydes in accordance with theinvention, may be illustrated by the follow- It is obvious from theequations that carbon chain of one alcohol 0nd. alcohol component: isregenerated as: such.

invention is: illustrated in the fiollowing examples.

Exampl'e 1 m al gave an average reacti n ime of 1.56 seconds. Theconversions to normal butyraldehyde were 112% and 15% respectively withultimate yields of better than Example 2- Example 3- 400. grams: ofacetal was vaporized and passed over a catalystcomprised of thoriaalumina gel in /s' pellets. The total catalyst volume wa-s: 1258 ml. andthe temperature was held: between 410 and 4 30 C. The contact timeemployed 1.64:8 seconds. Distillation of the product gave 26.0 gramsofnormal butyraldehyde in addit-ion to. unchanged acetal.

Example 4 Example 5 Four moles of dibutyl acetal were passed through areactor eor prise of .a. stainless steel tube 20 high #1" I.paeleedvwith 44; pellets. ofthoria; on: alumina heated to 430 C. Thefeed rate was '15 cc. per. minute-through a catalyst volume of 200 cc.The conversion tonultimate' yield of 65%.

3 Example 6 The reactor as described in Example was packed with magnesiaon Celite and six moles of diethyl butal was passed through at a rate of'l=1.5 cc. per minute. The temperature was 4l04 50 C. A conversion of28% was obtained to Z-ethylbutyraldehyde with an ultimate yield of 82%.A second run was made using steam as a diluent and hydrolysis of theacetal took place rather than rearrangement.

Example 7 Example 8 Using the reactor described in Example 1 andmolybdena on Celite at 450 C., diethyl acetal was fed at 12 cc. perminute through a catalyst bed of 200 cc. volume. Conversion ton-butyral-dehyde was 15% with ultimate yields of 80%. Azeotropicdistillation was used to separate butyraldehyde from unchanged acetal.

Example 9 In a second run carried out as in Example 8 but using vanadiaon Celite, conversion of acetal to n-butyraldehyde Was 18% with anultimate yield of 72%. Azeotropic distillation was used to separate then-butyraldehyde.

Example 10 In the same stainless steel reactor described in previousexamples was placed 200 cc. of copper on silica gel pellets. Diethylacetal was passed over this catalyst at 415-445 C. at a feed rate of12.5 cc. per minute to give 16% conversion to n-butyraldehyde with 70%yield.

Example 11 Diethyl hexal was passed over Ma" silver on alundum pelletsin the reactor previously described at a temperature of 450 C. A feedrate of 18 cc. per minute through the catalyst bed was maintained with atotal feed of 2 liters. A conversion of 30% to 2-ethylhexanal wasobtained with an ultimate yield of 81% From the foregoing examples itwill be obvious that a number of contact materials of well-known typesare suitable for carrying out the invention. While the contact materialsare not considered to be critical to the process we have found thatamong the more advantageous materials should be included alumina,alumina gel, molybdena on alumina, thoria on alumina and palladium onasbestos. Possibly the most advantageous contact material of which weare aware is silver on alundum. Thus,

v for a period of time between while it has been found that thetemperature range is critical to the reaction of the invention, thoseskilled in the art .will recognize that other contact materials notnamed herein may be found quite suitable for practice of the invention.

The high temperature range requires use of a certain amount of care incontrolling the time of exposure of the gasses to the hot contactmaterials. While the reaction time range is subject to variationsdependent upon the particular temperature and the particular acetal andcontact material employed, a period of time within the range of about0.5 to 3.0 second has been found more advantageous. I

The Celite" employed in the examples is a diatornaceous earth aspreformed and sold by the Johns- Manville Sales Corp.

We claim:

1. A method for the preparationof an aldehyde comprising the steps of(a) passing the of the formula vapor of an acetal RCH2CH(OCHR 2 whereinR and R are membersof the group consisting of hydrogen and lower alkylradicals over a suitable contact material heated to a temperature withinthe range 375 600 C. and (b) recovering by distillation from a productmixture thus formed an aldehyde having the formula R'CHzCHRCI-IO whereinR and R are as designated above.

2. A method as defined in claim 1 wherein the contact material is asubstance selected from the group consisting of alumina, alumina gel,molybdena on alumina, thoria on alumina, silver on alundum, andpalladium on asbestos.

3. A method as defined in claim 2 wherein the acetal vapor is subjectedto the heated contact material for a period within the range of about0.5 to 3.0 seconds.

4. A method for the preparation of propionaldehyde comprising the stepsof (a) passing the vapor of dimethyl acetal over a suitable contactmaterial selected from the group consisting of alumina, alumina gel,molybdena on alumina, thoria on alumina, silver on alundum, andpalladium on asbestos heated to a temperature within the range 375 -600C. and (b) recovering propionaldehyde by distillation from a productmixture thus formed.

5. A method as defined in claim 4 wherein the heated contact material ismolybdena on alumina, and the reaction is carried out at a temperatureof about 400 C.

0.5 and 3.0 seconds.

6. A method as defined in claim 4 wherein the contact material isalumina gel and the reaction is conducted at a temperature of about 400C. for a period of time within the range of about 0.5 to 3.0 seconds.

7. Amethod as defined in claim 4 wherein the contact material isthoria-alumina gel and the reaction is carried out at a temperaturewithin the range 410-430 C. for a period of time within the range ofabout 1.5 to 2.0 seconds.

' 8. A method for the preparation of isobutyraldehyde comprising thesteps of (a) passing the vapor of dimethyl propional over a heatedcontact material selected from the group consisting of alumina, aluminagel, molybdena on alumina, thoria on alumina, silver on alundum, andpalladium on asbestos at a temperature within the range 375 600 C. for aperiod within the range of about 0.5 to 3.0 seconds and (b) recoveringisobutyralclehyde by distillation from a product mixture thus formed.

9. A method as defined in claim 8 wherein the heated contact material ismolybdena on alumina, and the reaction is carried out at a temperatureof about 400 C. for a period of time between 1.5 and 2.0 seconds.

10. A method as defined in claim 8 wherein the heated contact materialis alumina gel and the reaction is conducted at a temperature of about400 C. for a period of time within the range of about 1.5 to 2.0seconds.

11. A method as defined in claim 8 wherein the heated contact materialis thoria-alumina gel and the reaction is carried out at a tempertaurewithin the range 410-430 C. for a period of time within the range ofabout 1.5 to 2.0 seconds.

12. A method for the preparation of an aldehyde comprising the steps of(a) heating the vapor of an acetal of the formula RCH2CH(OCHR' 2R'CHzCHRCHO 1?. A method as defined in claim 12 wherein the acetalReferences Cited in the file of this patent is dlmethyl acetal and thealdehyde is propionaldehyde.

UNIIED STATES PATENTS 14. A method as defined in claim 12 wherein the2,501,144 Saunders M 21, 1950 acetal is dimethyl propional and thealdehyde is isobutyraldehyde, 5 OTHER REFERENCES Richter; OrganicChemistry, 3rd ed., vol. 1 (1944), pp. 226-227, Elsevier Publishers

1. A METHOD FOR THE PREPARATION OF AN ALDEHYDE COMPRISING THE STEPS OF(A) PASSING THE VAPOR OF AN ACETAL OF THE FORMULA
 2. A METHOD AS DEFINEDIN CLAIM 1 WHEREIN THE CONTACT MATERIAL IS SUBSTANCE SELECTED FROM THEGROUP CONSISTING OF ALUMINA, ALUMINA GEL, MOLYBDENA ON ALUMINA, THORIAON ALUMINA, SILVER ON ALUNDUM, AND PALLADIUM ON ASBESTOS.